Transcript No Slide Title

Universita’ di Roma “La Sapienza”, Facolta’ di Ingegneria Elettrica, February 16, 2006
Power Line Communications:
Applications, Trends and Recent Modeling Results
Dr. Stefano Galli
Senior Scientist
Telcordia Technologies
[email protected]
http://www.argreenhouse.com/bios/sgalli/
Copyright © 2006 Telcordia Technologies. All Rights Reserved.
Outline
1) Applications: access, home network, in-vehicle, and beyond
2) PLC industry associations and IEEE standardization activities
3) Major research issues:
a) Coexistence
b) Channel modeling
4) Conclusions
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Power Line Communications
• First applications date back to early 1920s, on HV lines.
• The first standard is the European CENELEC EN 50065, which
mandates the use of the frequency range 3-148.5 kHz (1991).
• The first commercial attempt to use PLC for last mile access
dates back to 1997, when Nortel announced the NorWeb
partnership with United Utilities (a UK power utility company)
• Limited trials of broadband Internet access through power
lines were conducted in Manchester and NorWeb prototypes
were able to deliver data at rates around 1 Mbps.
• Cost and commercial viability became questionable and the
pilot project was terminated few years later in 1999.
• In the past few years, interest in the technology has picked up
again and possible applications have multiplied.
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Power Line Communications – outdoor
(From ADVANCE, March 2005)
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Power Line Communications – indoor
(From ADVANCE, March 2005)
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Power Line Communications – smart grid apps
(From ADVANCE, March 2005)
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Beyond Outdoor/Indoor…
• PLCs allows for easy in-vehicle networking:
– In any vehicles (from automobiles to ships, from aircraft to space
vehicles), separate cabling is used to establish the PHY of a local
command and control network which is becoming broadband
– The in-vehicle power distribution network may well perform
double-duty, as an infrastructure supporting both power delivery
and broadband digital connectivity.
– Weight, space and cost savings (aircraft, auto).
– “Plug & Play”
• PLCs as the enabler for truly pervasive and ad-hoc networks:
Just look around… power is everywhere
– Traffic lights, lamp posts, etc. can easily become network nodes
– Smart grid applications, better mains utilization and monitoring
– AMR, peak shaving, transformer monitoring, etc.
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Not Widespread Because …
•
•
•
•
•
•
•
PLC technology is still “young” and evolving
Do we really need another access solution?
Do the power utility companies really want to enter telecom?
Is there a solid business case?
Deregulation and liberalization are fairly recent
Lack of standardization and interoperability of products
Not everybody convinced of the technology:
• PHY and MAC layers still a big issue
• Until recently, the available channel models could not predict
accurately the channel transfer function a priori!!
• Electromagnetic compatibility issues
• Necessity of hybrid infrastructures, between PLC-based
networks and existing wireless/fiber/copper-based ones.
Nevertheless, today PLCs are experiencing a renaissance !
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From Brett Kilbourne, UPLC Conference, Sep. 2005
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World Trends in PLCs
(From ADVANCE, March 2005)
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HomePlug Powerline Alliance
• 3Com, Cisco, Compaq, Conexant, Enikia, Intel, Intellon,
Motorola, (Panasonic), AMD, RadioShack, Texas Instruments
• A non-profit organization
• Provides a forum for the creation of open specification for home
power line networking products and services
• Traditionally focused on the indoor environment only.
• Two indoor specifications: 1.0 and A/V.
• Recently, the HomePlug Access BPL Working Group initiative
was recently launched. HomePlug BoPL refers to the outdoor
environment of power lines. Necessity of addressing outdoor:
• wires used in the home are the same of those coming from
outside, and the utilized spectrum is the same
• Home networks coming off a common transformer may
interfere with each other.
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Universal Powerline Association (UPA)
• Ambient Corporation, Ascom Powerline Communications,
Corinex Communications, DS2, Electricite de France, IlevoSchneider Electric Powerline Communications, Itochu, Sumitomo
Electric Industries, and TOYOCOM.
• A non-profit organization
• Trade association working to harmonize global standards and
regulations, and to deliver UPA certified products which comply
with agreed specifications. Covers both home and access.
• In May 2004, the UPA interest group was established and a
Memorandum of Understanding was signed in September 2004.
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Consumer Electronics Powerline Comms Alliance (CEPCA)
 Consumer Electronics Powerline Communication Alliance is a
nonprofit corporation with the following members: Hitachi, Sony,
Panasonic Toshiba, Mitsubishi, Yamaha, Pioneer.
 Established to promote and continuously advance high speed
PLC technology to utilize and implement a new generation of
consumer electronics products through the rapid, broad and
open industry adoption of CEPCA Specifications
 The Purpose of Consumer Electronics Powerline Communication
Alliance is to
– Completely remove the mutual interference between PLC systems
that employ different technologies but use the same bands
– Create and standardize technical specifications that enable
different PLC systems to coexist and achieve optimal
performance
– Enable creation CEPCA implementations that become an
essential function to the widespread usage of CE devices
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Open PLC European Research Alliance (OPERA)
• It is a European R&D Project with a budget of about 20 M Euros.
• Scientific and technological objectives of the project are:
• Improve current PLC systems, both conditioning the power grid
(using couplers and filters) and improving PLC equipment.
• Develop optimal solutions for connection of the PLC access
networks to the backbone networks.
• Standardization of PLC systems.
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United Power Line Council (UPLC)
• The United Power Line Council (UPLC) is an alliance of electric
utilities and technology companies working together to drive the
development of Broadband over Power Line (BPL) in a manner
that helps utilities and their partners succeed.
• UPLC's efforts are focused in four strategic areas: Business
Opportunities, Regulatory & Legislative Advocacy, Technical
Operability and Utility Applications .
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The Role of IEEE
• The first society to promote standardization was PES, then came
the others (EMS, AP, ComSoc)
• In October 2004, ComSoc created a Technical Sub-Committee on
PLCs (sub-committee under Emerging Technology).
• In December 2005, The BoG of IEEE ComSoc upgraded the subcommittee to a Full Fledged IEEE Technical Committee:
• S. Galli, Telcordia Technologies, Chair
• L. Lampe, University of BC, Vice-Chair and Events Liaison
• R. Fantacci, University of Florence, Vice-Chair
• Haniph Latchman, University of Florida, Publications Liaison
• Jim Mollenkopf, Current Technologies (VP), Standards Liaison
• Peter Griffin, RadioShack Corporation, External Relations
• Broad consensus: 70+ members (industry, academia, retail)
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The Role of the IEEE ComSoc Technical Committee
• The interests of the committee span all the areas of PLCs, e.g.,
access, home networking, and in-vehicle applications.
• The committee will organize events in the PLC area, sponsor PLC
conferences, contribute to the organization of technical events
along ComSoc flagship conferences, and will promote the
realization of special issues on leading ComSoc journals and
magazines.
• The committee also promotes ComSoc involvement in the
development of IEEE Standards in the area of PLCs
• Jim Mollenkopf nominated as Co-Chair BPL PHY-MAC Working Group
• Participates to the BoPL study group, to standardization efforts;
will organize events, special issues, publications, etc.
• IEEE Communications Magazine special issue: “Power line local area
networking,” April 2003
• IEEE Communications Magazine special issue: “Broadband is Power:
Internet Access Through the Power Line Network ,” May 2003
• IEEE Journal on Selected Areas in Communications special issue on Power
Line Communications, July 2006
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IEEE Standardization Activities
P1901
•
Focuses on MAC/PHY aspects and was officially approved by
the IEEE Standards Board on 4 June 2005.
•
The Working Group is co-chaired by Jim Mollenkopf (Current
Technologies) and Jean-Philippe Faure (Snider Electric).
•
P1901 operates as an entity standards development group,
where all members are organizations instead of individuals.
•
As of this date, 28 entities are members. The group has agreed
use cases for in-home and access BPL, and will be developing
detailed requirements in the coming months.
•
Meetings are open to all (members and non-members), and the
next meeting is in March 26-30 during ISPLC 2006 (Orlando
Florida).
• More information can be found at the P1901 website at:
http://grouper.ieee.org/groups/1901/index.html
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IEEE Standardization Activities
P1775
•
The P1775 effort focuses on specific measurement issues
associated with BPL emissions.
•
This group is chaired by Aron Viner.
•
This group has formed three task groups focused on immunity
measurements methods, emissions measurements methods,
and overall network description.
•
The next P1775 meeting will be during ISPLC 2006.
•
Further information is available from the chair at
[email protected]
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IEEE Standardization Activities
P1675
•
P1675 is focused on developing standards for equipment testing
and installation.
•
This effort is chaired by Terry Burns.
•
An initial draft has been produced, and is currently being
reviewed and revised by the Working Group.
•
The next P1675 meeting is scheduled during ISPLC 2006.
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Coexistence Issues
From Mike Stelts (CEPCA), UPLC Conference, Sep. 2005
• There is no demarcation between access and in-home power
line cables  it is a bus running from sub-station transformer
to every plug in the home
• Access signals and in-home signals must co-exist
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Coexistence Issues
From Mike Stelts (CEPCA), UPLC Conference, Sep. 2005
• Power line cables are a shared medium, like coax cable and
unlike DSL
• Signals in your home become interference for your neighbor, and
viceversa
• Not only complicated MAC problem, but also security issues
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Coexistence Issues – a dilemma for standardization
• IEEE standardization for PLCs (P1901) has started few months
ago, and Ballot Draft of standard is expected by mid 2006
• There are today two philosophies:
• one technology for everything (all applications) and also for
everywhere in the world
• multiple technologies, but all constrained to coexist with each
other anywhere and everywhere.
• Both positions seem extreme:
• Difficult to envision only one technology for everything and
everywhere given the wide variability of environments
• Difficult to envision optimized solutions if so many constraints
about coexistence are imposed.
• Probably, other approaches should be pursued:
• Network segmentation, e.g. at the meter
• Software Defined Radio approach
• Consumer pays premium of the DSP and the hardware of the SDR in
the consumer electronic equipment, but has capability to change or
upgrade its modem by downloading new software.
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Channel Modeling Issues: Wide Variability of Environment
• International:
– wiring system uses a star (e.g., a single cable feeds all of the
wall outlets in one room only) or tree arrangement
– ground bonding at the main panel
• Europe:
– two wire (ungrounded) or three wire (grounded) outlets
– If three phase supply is used, separate rooms in the same
apartment may be on different phases
• UK exceptions:
– special rings: a single cable runs all the way round part of a
house interconnecting all of the wall outlets; a typical house
will have three or four rings.
– neutral not grounded in the home
– New builds: three phase with four of five wires (neutral, ground)
– Problematic old wiring: two-wire 1 phase, neutral and ground share
common wire
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International Harmonization
• Wiring and grounding come in many flavors, and this makes
modem design much more challenging.
• However, international harmonization is happening:
– Typical outlets have three wires: hot, neutral and ground
– Classes of appliances (light, heavy duty appliances, outlets, etc.)
fed by separate circuits
– Neutral and ground separate wires within the home, except for the
main panel where they are bonded
Although complex topologies may exist, today’s
regulations can simplify analysis of signal transmission
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Wiring and Grounding Practices
SERVICE
PANEL
FEED
RECEPTACLE CIRCUITS
15-20 amps, branching, and
symmetric geometry for B&W
LIGHTING CIRCUITS
Non-symmetric geometry
for B&W
GROUND
BONDING
EMBEDDED APPLIANCES
50 amps, non-branching, and symmetric
geometry for B&W
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Inside wiring environment
NM-B
BX
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Inside wiring environment
CBW
CBG
CWG
CABLE
Zdif1
Zdif2

Zpr

ohms
ohms
ns/m
ohms
ns/m
14/2 NM-B
136±10
9.7±0.6 58±4
9.6±0.8
12/2 NM-B
121±6
9.3±0.3 47±4
9.4±0.3
12/2 BX
73
52
2×2.5/1.5(UK) 108
10.7
46
11.3
2/2/2 TW
74
9.5
46
9.5
14/3 NM-B
87±2
94±1
11.0
30
11.0
12/3 NM-B
89±1
92±1
10.2
28
10.6
12/3 TW
136
136
10.2
45
10.2
105
79
9.9
30
9.7
8/3 NM-B
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Wiring and Grounding Practices
SERVICE
TRANSFORMER
SERVICE
DROP
HOT
Typical service panel, showing
bonding between the neutral and
the ground cable through RSB.
RTN
CIRCUIT
BREAKERS
BLK
BLK
L2
L3
WHT
WHT
RSB
GND
RSB
GND
Paradoxically, grounding and bonding has been completely
ignored in indoor PLC modeling
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Effects of Bonding on Signal Propagation
Ground bonding introduces non negligible resonant modes due to
pair-mode excitation.
LOSS
3dB/DIV
Topology without bonding
B
0.3
FREQUENCY ( MHz)
30.0
Same topology with bonding
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Channel Modeling Approaches
Two-Conductor Transmission Line Model
Hooijen - ISPLC’98
• Straightforward approach, follows TPC/coax modeling
• Frequency domain model
• Transfer function can be computed a priori
• Limitations:
• Knowledge of whole topology is needed
• Accuracy of results depend on accuracy of cable models
• Incomplete model, presence of third wire not included so that
wiring and grounding practices not explicitly accounted for
• Some aspects of signal propagations cannot be explained
with this model
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Channel Modeling Approaches
Multipath Model
Phillips, and Dostert & Zimmermann - ISPLC’99, T-COM’02
The multipath nature arises from the presence of several branches
and impedance mismatches that cause reflections.
B
B(f)
LAB
A2(f)
LXA
X
LAY
Y
A1(f)
A
d 0  L XA  L AY
Direct path XAY (i=0): 
 g 0  1   A1 

di  LXA  2iLAB  L AY
Secondary paths XABA(BA) Y(i>0): 
i 1




g

1


1




B

A
1
A
2
B
A
2
 i
i-1
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Channel Modeling Approaches
N
H ( f )   gi e j 2f i e ( f )di
i 1
gi: is a complex number that depends on the topology of the link;
(f) is the attenuation coefficient (skin effect and dielectric loss);
i is the delay associated with the ith path;
di is the path length;
N is the number of non-negligible paths.
The multipath model is a good model, but has some limitations:
• modeling is based on parameters that can be estimated only
after the actual channel transfer function has been measured
• wiring and grounding practices not explicitly accounted for, but
“phenomenologically” included
• computational cost in estimating the delay, amplitude and
phase associated with each path (time-domain model) 
drawback for some indoor/in-vehicle channels.
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Effects of Bonding on Signal Propagation
B
Measurements
(when bonding present)
4dB/DIV
0
-5
-10
LOSS
Magnitude of Transfer Function (dB)
Current Models
(no
bonding)
5
-15
-20
-25
0
5
10
15
20
Frequency in MHz
25
30
0.3
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FREQUENCY ( MHz)
30.0
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Recent Results on Channel Modeling: MTL
Multi-Conductor Transmission Line Model
Galli & Banwell - ISPLC’01, T-PD’05 Part I - II
• Based on Multi-conductor Transmission Line Theory and Modal
Decomposition: can take into account multi-conductor nature of
PL cables, as well as wiring and grounding practices.
• Transfer function can be computed a priori
• Frequency domain model (limited computational complexity).
• Allows to unveil interesting and useful properties of the PLC, e.g.
superposition of resonant modes, isotropy of channel.
• Limitations:
• Knowledge of whole topology is needed
• Accuracy of results depend on accuracy of cable models
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Recent Results on Channel Modeling: MTL
Three-conductor Analysis
• A three-conductor cable supports six propagating modes (TEM
approximation): three spatial modes (differential, pair and
common modes) each for two directions of propagation.
• The differential mode current, generally the desired signal.
• The pair-mode current (flowing between ground and the
white/black wires “tied together”). This mode is excited due to
certain wiring and grounding practices.
• The third common mode current Icm represents overall cable
current imbalance, which creates a current loop with earth
ground. Lossy mode, can be neglected.
Pair-mode has been completely neglected in previous models
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Recent Results on Channel Modeling: MTL
MTL modeling requires crossing several layers of abstraction:
• Derive the differential mode and pair mode circuit models of
power line link
• Tie the two modes through a transformer
• Describe each circuit models as cascaded two-port networks
• Obtain transfer function using transmission matrices
Treat with same formalism
both grounded and ungrounded links
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MTL Approach: Better Accuracy
B
Current models
(no bonding)
MTL model
4dB/DIV
0
-5
-10
LOSS
Magnitude of Transfer Function (dB)
5
-15
-20
-25
0
5
10
15
20
Frequency in MHz
25
30
0.3
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FREQUENCY ( MHz)
30.0
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Concluding Remarks
• We have today a better understanding of the PL channel
• PL channel more deterministic than originally thought
– Determinism should be exploited for transceiver optimization
• Plethora of grounding and wiring practices, but harmonization of
regulations can simplify analysis of signal transmission
– Wiring and grounding practices must be taken into account
• Lack of traditional research funding has kept PLC research out of
academia, so that most work has been done within an industrial
environment and has been directed towards winning skepticism
– Lack of a solid theoretical approach!
• System optimization is challenging
– PLCs is one of the most inter-disciplinary fields we have
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